In recent years, in view of global environmental protection and cost effectiveness, self-ballasted fluorescent lamps with electrodes which are about five times as effective as incandescent lamps have been widely used to substitute the incandescent lamps in houses, hotels and other places. Such a self-ballasted fluorescent lamp with electrodes is disclosed in Japanese Laid-Open Publication No. 2001-196194, for example. Self-ballasted fluorescent lamps include ballasts and bases so that the lamps can be directly replaced with incandescent lamps in terms of structure.
In addition to the existing self-ballasted fluorescent lamps with electrodes, electrodeless self-ballasted fluorescent lamps are becoming widespread recently. The absence of electrodes eliminates wearing out of electrodes, and thus the electrodeless fluorescent lamps have a feature of longer life than that of the self-ballasted fluorescent lamps with electrodes. Therefore, the electrodeless fluorescent lamps are expected to become more and more widespread in future. Such an electrodeless self-ballasted fluorescent lamp is disclosed in Japanese Laid-Open Publication No. 9-320541, for example.
The electrodeless fluorescent lamps were mainly used for public lighting (e.g., street lighting) previously. However, after the appearance of electrodeless self-ballasted fluorescent lamps, the electrodeless fluorescent lamps came to be also used as a replacement of incandescent lamps in hotels and other places. Therefore, more attention needs to be paid to prevention of shattering caused by possible fracture than in conventional lamps.
Now, FIG. 20 shows the electrodeless self-ballasted fluorescent lamp disclosed in Japanese Laid-Open Publication No. 9-320541. FIG. 21 shows the self-ballasted fluorescent lamp with electrodes disclosed in Japanese Laid-Open Publication No. 2001-196194, for comparison.
As shown in FIG. 20, a spherical bulb 303 has a cavity portion for inserting an induction coil (306 and 307) therein. Though luminous gas is enclosed in the bulb 303, the bulb 303 is under a reduced pressure of several Pa to several hundred Pa. Films 301 and 302 shown in FIG. 20 are a conductive film and a luminophor, respectively. If the bulb 303 is broken in part, an implosion occurs toward the center of the bulb because of the reduced pressure inside the bulb 303. Accordingly, shattering is considered to occur more heavily than in a self-ballasted fluorescent lamp with electrodes.
Specifically, with respect to the self-ballasted fluorescent lamp with electrodes, though the inside of a tubular bulb 71 is under a reduced pressure as in a general fluorescent lamp, the tubular bulb 71 is surrounded with air and a globe 75 is disposed around the periphery thereof, as shown in FIG. 21. Accordingly, even if the bulb 71 is broken, the shatters are hold within the globe 75. Further, even if the globe 75 absorbs the shock of the shatters and is broken, no implosion occurs because the inside of the globe 75 is not under a reduced pressure. Even in the case of a lamp without the globe 75, as long as the lamp is a self-ballasted fluorescent lamp with electrodes, the force produced by the difference between the inside of the bulb and atmospheric pressure at the shattering is widely scattered along the center axis of the bulb because of the tubular shape of the bulb, so that the force is reduced as compared to the electrodeless self-ballasted fluorescent lamp in which the force is concentrated at the center of the spherical bulb. As a result, the shattering is suppressed in such a case.
Therefore, it is a main object of the present invention to provide a self-ballasted fluorescent lamp and an electrodeless discharge lamp operating apparatus capable of preventing shattering effectively even in a case where the lamp is broken and shatters.